1. Field of the Invention
Embodiments of the present invention relate to a liquid crystal display (LCD) device, and more particularly to a method of driving the LCD device. Embodiments of the present invention are suitable for a wide scope of applications. In particular, embodiments of the present invention are suitable for increasing a light transmittance without distorting a color of the LCD device.
2. Description of the Related Art
Generally, an LCD device controls light transmittance of liquid crystal cells in accordance with video signals to thereby display a picture. An active matrix LCD device uses a switching device at each liquid crystal cell to improve the ability of displaying moving picture. The switching device used for the active matrix LCD device can be a thin film transistor (“TFT”) as shown in FIG. 1.
Referring to FIG. 1, the active matrix LCD device converts a digital input data into an analog data voltage in accordance with a gamma reference voltage and supplies the analog data to a data line DL. Concurrently, the active matrix LCD device supplies a scanning pulse to a gate line GL, thereby charging a liquid crystal cell Clc.
A gate electrode of the TFT is connected to the gate line GL, a source electrode is connected to the data line DL, and a drain electrode of the TFT is connected to a pixel electrode of the liquid crystal cell Clc and one terminal of a storage capacitor Cst. A common electrode of the liquid crystal cell Clc is supplied with a common voltage Vcom.
When the TFT is turned-on, the storage capacitor Cst charges a data voltage applied from the data line DL to maintain a constant voltage at the liquid crystal cell Clc. If the gate pulse is applied to the gate line GL, the TFT is turned-on to define a channel between the source electrode and the drain electrode, thereby supplying a voltage on the data line DL to the pixel electrode of the liquid crystal cell Clc. In this case, liquid crystal molecules of the liquid crystal cell Clc are arranged by an electric field between the pixel electrode and the common electrode to modulate an incident light.
FIG. 2 is a block diagram showing a configuration of the related art LCD device. Herein, R represents red, G represents green, B represents blue, C represents cyan, W represents white, M represents magenta, and Y represents yellow. Referring to FIG. 2, an LCD device 100 includes an LCD panel 110 with a thin film transistor (TFT) driving the liquid crystal cell Clc at an crossing of data lines DL1 to DLm and gate lines GL1 to GLn crossing each other, a data driver 120 supplying a data to the data lines DL1 to DLm of the LCD panel 110, a gate driver 130 supplying a scanning pulse to the gate lines GL1 to GLn of the LCD panel 110, a gamma reference voltage generator 140 providing a gamma reference voltage to the data driver 120, a backlight assembly 150 irradiating a light onto the LCD panel 110, an inverter 160 applying an alternating current voltage and a current to the backlight assembly 150, a common voltage generator 170 providing a common voltage Vcom to the common electrode of the liquid crystal cell Clc of the LCD panel 110, a gate driving voltage generator 180 providing a gate high voltage VGH and a gate low voltage VGL to the gate driver 130, and a timing controller 190 controlling the data driver 120 and the gate driver 130.
The timing controller 190 supplies a digital video data RGB supplied from a system to the data driver 120. Furthermore, the timing controller 190 generates a data driving control signal DDC and a gate driving control signal GDC using horizontal/vertical synchronizing signals H and V in response to a clock signal CLK to supply them to the data driver 120 and the gate driver 130, respectively. Herein, the data driving control signal DDC includes a source shift clock SSC, a source start pulse SSP, a polarity control signal POL and a source output enable signal SOE, etc. The gate driving control signal GDC includes a gate start pulse GSP and a gate output enable signal GOE, etc.
The LCD panel 110 has a liquid crystal material formed between two glass substrates (not shown). On the lower glass substrate of the LCD panel 110, the data lines DL1 to DLm and the gate lines GL1 to GLn perpendicularly cross each other. Each crossing of the data lines DL1 to DLm and the gate lines GL1 to GLn is provided with the TFT. The TFT supplies a data on the data lines DL1 to DLm to the liquid crystal cell Clc in response to the scanning pulse. The gate electrode of the TFT is connected to the gate lines GL1 to GLn while the source electrode thereof is connected to the data line DL1 to DLm. Further, the drain electrode of the TFT is connected to the pixel electrode of the liquid crystal cell Clc and to the storage capacitor Cst.
The TFT is turned-on in response to the scanning pulse applied, via the gate lines GL1 to GLn, to the gate terminal thereof. Upon turning-on of the TFT, the video data on the data lines DL1 to DLm is supplied to the pixel electrode of the liquid crystal cell Clc. The data driver 120 supplies a data to the data lines DL1 to DLm in response to the data driving control signal DDC supplied from the timing controller 190. Further, the data driver 120 samples and latches the digital video data RGB from the timing controller 190, and then converts it into an analog data voltage capable of representing a gray level at the liquid crystal cell Clc of the LCD panel 110 on the basis of the gamma reference voltage supplied from the gamma reference voltage generator 140, thereby supplying it the data lines DL1 to DLm.
The gate driver 130 sequentially generates the scanning pulse, that is, the gate pulse in response to the gate driving control signal GDC and the gate shift clock GSC supplied from the timing controller 190 to supply them to the gate lines GL1 to GLn. In this case, the gate driver 130 determines a high level voltage and a low level voltage of the scanning pulse in accordance with the gate high voltage VGH and the gate low voltage VGL supplied from the gate driving voltage generator 180.
The gamma reference voltage generator 140 receives a high-level power voltage VDD to generate a positive gamma reference voltage and a negative gamma reference voltage and output them to the data driver 120.
The backlight assembly 150 is provided at the rear side of the LCD panel 110, and is radiated by an alternating current voltage and a current supplied from the inverter 160 to irradiate a light onto each pixel of the LCD panel 110.
The inverter 160 converts an internally generated square wave signal into a triangular wave signal, and then compares the triangular wave signal with a direct current (DC) power voltage VCC externally supplied to generate a burst dimming signal proportional to the result. If the burst dimming signal determined in accordance with the rectangular wave signal of the interior of the inverter 160 is generated, then a driving integrated circuit IC (not shown) controlling a generation of the AC voltage and a current within the inverter 160 controls a generation of AC voltage and current supplied to the backlight assembly 150 in accordance with the burst dimming signal.
The common voltage generator 170 receives a high-level power voltage VDD to generate the common voltage Vcom and supplies it to the common electrode of the liquid crystal cell Clc provided at each pixel of the LCD panel 110.
The gate driving voltage generator 180 is supplied with the high-level power voltage VDD to generate the gate high voltage VGH and the gate low voltage VGL, and supplies them to the gate driver 130. Herein, the gate driving voltage generator 180 generates a gate high voltage VGH greater than a threshold voltage of the TFT provided at each pixel of the LCD panel 110 and a gate low voltage VGL less then the threshold voltage of the TFT. The gate high voltage VGH and the gate low voltage VGL generated in this manner are used for determining a high level voltage and a low level voltage of the scanning pulse generated by the gate driver 130, respectively.
The LCD having such configurations and functions can be implemented using a variety of driving methods depending on whether or which color filter is used in the LCD panel and the type of light source applied to the LCD panel 110. A first related art the LCD device 100 uses R, G, and B color filters. In the first related LCD device, each pixel is partitioned into an R sub-pixel, a G sub-pixel, and a B sub-pixel using R, G, and B color filters in the LCD panel 110. Thus, in the first related art LCD device 100, a white lamp generating only white light is used as a light source for the backlight. Accordingly, white light irradiated from the white lamp is spatially divided by the R, G, and B color filters amongst the R, G and B sub-pixels. Accordingly, about 30% of the light from the backlight is irradiated by each of the R, G, and B color filters through the corresponding R, G or B sub-pixel.
A second related art LCD device 100 does not use a color filter in the LCD panel and uses a Field sequential (FS) driving method for color implementation. In the second related art LCD device 100, the pixels are not spatially divided into R, G and B sub-pixels. Thus, an R light source, a G light source, and a B light source are provided in the backlight of the LCD device 100. The R light source generates an R light, the G light source generates a G light, and the B light source generates a B light, respectively. Since the pixels are not spatially divided into color sub-pixels, the LCD device 100 performs a time division by sequentially irradiating the R light, the G light, and the B light to display R, G, and B colors, respectively. Moreover, because the pixels are not spatially divided into color sub-pixels, the FS driving method provides about 100% transmittance for each of the R light, the G light, and the B light. Furthermore, the LCD device 100 of the FS driving method provides a higher aperture ratio than the first related art LCD device.
A third related art LCD device 100 uses G and M color filters in the LCD panel for color implementation. In the third related art LCD device, each pixel is divided into a G sub-pixel and an M sub-pixel using G and M color filters provided within the LCD panel 110. Thus, in the LCD device 100, the backlight includes a C light source and a Y light source generating a C light and a Y light, respectively. Moreover, each frame is divided into first and second subframes sequentially displayed. Thus, if the frames are driven at a driving frequency of about 60 Hz, the corresponding first and second subframes are driven at a frequency of about 120 Hz.
During the first subframe, the third related art LCD device 100 supplies a C data and a B data to the G sub-pixel and the M sub-pixel, respectively, and irradiates a C light onto the G sub-pixel and the M sub-pixel. Thus, each of the G and M filters transmits 50% of the incident light during the first subframe.
During the second subframe, the third related LCD device 100 supplies a G data and an R data to the G sub-pixel and the M sub-pixel, respectively, and at the same time irradiates a Y light into the G sub-pixel and the M sub-pixel. Thus, each of the G and M filters transmits 50% of the incident light during the second subframe.
Thus, by reducing the number of color filters in the LCD panel, a light transmittance and an aperture ratio are improved. Moreover, when the R, G, and B color filters are used, one frame is divided into three subframes. Accordingly, the three subframes are driven at a frequency of about 180 Hz. On the other hand, when only the G and M color filters are used, each frame is divided into two subframes. Accordingly, the two subframes are driven at a driving frequency of about 120 Hz. Thus, the subframes in LCD panel using G and M color filters can be driven at a reduced frequency. However, a light transmittance of the G sub-pixel and the M sub-pixel needs be improved.